1. Technical Field
The present invention relates to polyacetal resins having high rigidity, excellent creep property, high surface hardness and excellent sliding property.
2. Prior Art
Polyacetal resins have excellent properties in terms of mechanical property, thermal property, electric property, sliding property, molding property, etc. and have been widely used in electric appliances, automobile parts, precision instrument parts, etc. mostly as constituting materials, mechanical parts, etc. thereof. However, as a result of expansion of the fields to which polyacetal resins are used, there are some cases where further improvements in rigidity and creep property are demanded. As a means for improving such physical properties, a method where fibrous fillers are filled inpolyacetal resin, a method where a comonomer amount is reduced in the case of polyacetal copolymers, etc. have been known. However, in filling the fibrous filler, problems such as a poor appearance of the molded product and a lowering of the sliding property are resulted while, in the means of reducing the amount of comonomers, problems such as a lowering of thermal stability of the polymer are resulted and, therefore, they do not always meet with the demands.
In view of such problems in the prior art, the present inventors paid their attention to an essential improvement in rigidity and creep property of the polymer by modification of the polymer structure itself.
In the meanwhile, with regard to modification of the polymer structure itself, there are disclosures in JP-A3-170526 and others on modified polyacetal copolymers prepared by copolymerization of trioxane, at least one cyclic ether compound selected from ethylene oxide, 1,3-dioxolane, 1,3-dioxepane, 1,3,5-trioxepane and 1,3,6-trioxocane, and at least one compound selected from glycidyl phenyl ether, styrene oxide and glycidyl naphthyl ether. However, an object of the modified polyacetal copolymers is to improve the molding property, particularly the high cycling property, by an increase in crystallizing rate and, in addition, the effect of improving the rigidity by those copolymers has been found to be not so satisfactory according to the test by the present inventors.